CA2063374C - Composition for controlling oxides of nitrogen - Google Patents
Composition for controlling oxides of nitrogenInfo
- Publication number
- CA2063374C CA2063374C CA002063374A CA2063374A CA2063374C CA 2063374 C CA2063374 C CA 2063374C CA 002063374 A CA002063374 A CA 002063374A CA 2063374 A CA2063374 A CA 2063374A CA 2063374 C CA2063374 C CA 2063374C
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- CA
- Canada
- Prior art keywords
- chemical additive
- weight
- concentration
- composition
- aminotetrazole
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
- C06B29/00—Compositions containing an inorganic oxygen-halogen salt, e.g. chlorate, perchlorate
- C06B29/02—Compositions containing an inorganic oxygen-halogen salt, e.g. chlorate, perchlorate of an alkali metal
- C06B29/16—Compositions containing an inorganic oxygen-halogen salt, e.g. chlorate, perchlorate of an alkali metal with a nitrated organic compound
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- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
- C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
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- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06C—DETONATING OR PRIMING DEVICES; FUSES; CHEMICAL LIGHTERS; PYROPHORIC COMPOSITIONS
- C06C9/00—Chemical contact igniters; Chemical lighters
-
- C—CHEMISTRY; METALLURGY
- C06—EXPLOSIVES; MATCHES
- C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
- C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
- C06D5/06—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets by reaction of two or more solids
Abstract
A gas generant composition devoid of azides which yields solid combustion products which are easily filtered rendering the gases useful for inflating automobile occupant restraint bags and further providing a reduction in the amount of toxic oxides of nitrogen in the produced gases.
Description
BACKGROUND OF THE INVENIION
Field Of The Invention Gas genpr~ting colllpositions for infl~ting occllp~nt lc~ t devices of over-the-road vehicles have been under development worldwide for many years and numerous patents have been granted thereon. l~ se of strict requirements relating to toxicity of the infl~tin~ gases, most gas generants now in use are based on inorganic azides, and especially sodium azide. One advantage of such known sodium azide gas generants is that the solid combustion products thereof generally produce a slag or "clinkers" which are easily filtered, resulting in a relatively clean gas. The ability of a gas generant to form a slag is a great advantage when the gases are used for inflation purposes, especi~lly when the gases must be filtered as in the inflation of an automobile oc~;up~nl fcslldint bag.
However, the use of the sodium azide, or other azides as a practical matter, results in extra expense and risk in gas generant m~mlf~ctllre due to the extreme JJ:vs toxicity of unfired azides. In addition, the potential hazard and disposal problem of unfired inflation devices must be considered. Thus, a nonazide gas generant exhibits a significant advantage over an azide-based gas generant because of such toxicity related concerns.
A fundamental problem that must be solved when using nonazide based gas generants is that it is easier to formulate slagging gas generants based on sodium azide than nonazide types because the combustion temperature is relatively low with azide-based gas generants. For example, the combustion temperature of a sodium azide/iron oxide slagging type generant is 969C (1776F) whereas, nonazide slagging type generants heretofore known have exhibited a combustion temperature of 1818C (3304F). Moreover, many common solid combustion products which might be expected from nonazide gas generants are liquids at the combustion temperature exhibited and are therefore difficult to filter out of the gas stream. For example, potassium carbonate melts at 891C and sodium silicate melts at approximately 1100C.
The formation of solid combustion products which coalesce at high combustion temperatures, and at high gas flow rates, requires a special combination of materials. Early attempts at formulating nonazide gas generants resulted in semi-solid combustion products that were difficult to filter. It has been found that combustion products which are liquid at the combustion temperature must be cooled until solidified before _ 3 filtering is successful because liquid products penetrate and clog the filter. It has also been found that cooling of the liquid combustion products results in cooling of the gas, which require~ the use of more gas generant. A cooled gas is relatively less efficient for inflation purposes, especially with an aspirator system. The additional gas generant, in turn, requires more cooling and an additional filter as well as a larger combustion chamber.
Mo~t azide-free, gas generant compositions provide a higher yield of gas (moles of gas per gram of gas generant) than conventional occupant restraint gas generants.
Although azide-free gas generating compositions offer numerous advantages over azide-based gas generants, it has been found difficult to produce gases which have sufficiently low levels of toxic substances. The toxic gases which are the most difficult to control are the oxides of nitrogen (NOx) and carbon monoxide (CO).
Most azide-free gas generants consi~t of carbon and nitrogen containing ingredientY which, upon combu~tion, produce small, but undesirable levels of NOx and CO in addition to the desired products, nitrogen and carbon dioxide.
In combustion processes involving compoundq containing both nitrogen and carbon it is possible to reduce or eliminate the CO by increasing the ratio of oxidizer to fuel. In this case, the extra oxygen oxidizes the CO to carbon dioxide. Unfortunately, 2063~74 L~
however, this approach results in increa~ed amount~ of NOx.
The ratio of oxidizer to fuel may also be lowered to eliminate excess oxygen and provide a fuel rich condition which reduces the amount of NOx produced. This approach, however, results in increased amounts of CO.
Even though it is possible, by means of chemical equilibrium calculationq, to find conditions of temperature~, pressure and gas generant compo~ition which could reduce both NOx and CO to nontoxic levels it has been very difficult to accomplish this result in actual practice.
The aforesaid problems are solved by the present invention, which discloses several type~ of nonazide ga~ generants that yield solid combustion products which form a ~lag or clinkers at the relatively high combustion temperature~ encountered with nonazide gas generants. The gas generants disclosed herein allow the u~e of ~imple, relatively inexpensive filter~ which cool the gas less and result in better pumping in an aspirated ~ystem. Taken together, these factor~ result in a simpler, less ëxpen~ive and smaller airbag inflation sy~tem.
A problem solved by a preferred embodiment of this invention i~ that the NOx is controlled by mean~
which are effective even though a limited amount of excess oxygen i8 present. This allows reduction of the CO level by the exce~s oxygen while, at the same time, lowering the NOx concentration to acceptable values.
DESCRIPTION OF THE PRIOR ART
An example of prior art teaching~ relating to the ~ubject matter of the instant invention is found in European Patent No. 0,055,547 entitled, "Solid Composition~ for Generating Nitrogen, The Generation of Nitrogen Therefrom and Inflation of Ga~ Bag~
Therewith". Thiq patent describes use of alkali or alkaline earth metal salt~ of a hydrogen-free tetrazole compound and oxidizerq of sodium nitrate, sodium nitrite and pota~qium nitrate or alkaline earth nitrates. A filter design is disclosed which utilizeq fiberglass fabric that forms a tacky surface for particle entrapment. The filter ha~ regions which cool and conden~e combustion solids. It iq obvious from the disclo~ure and from the nature of the ga~ generating compositions that the qolids produced do not form a qlag and are difficult to filter.
European Patent No. 0,055,904 entitled, "Azide Free Compo~ition~ for Generating Nitrogen, The Generation of Nitrogen Therefrom and Inflation of Ga~
Bag~ Therewith" deqcribes a filter used for particle entrapment. Oxidizers which contain no oxygen are used, and no mention of slag formation is made.
German Patent 2,004,620 teaches compoqitions of organic qalt~ (aminoguanidine) of ditetrazole and azotetrazole that are oxidized using oxidizers such as barium nitrate or potassium nitrate. However, no compo~itions are mentioned which would lead to ~lag formation.
U S. Patent 3,947,300 entitled, "Fuel for Generation of Nontoxic Propellant Gases" discloses the use of alkali or alkaline earth metal azides that can be oxidized by practically any stable anhydrous oxidizing agent. The ratio of ingredients is selected to assure the formation of glasQ-like silicates with "as low a melting or softening point as possible"
(column 2, lines 62-63 and column 4, lines 67-68).
These silicates would be very difficult to filter in a high temperature system.
U.S. Patent 4,376,002 entitled, "Multi-Ingredient Gas Generators" teaches the use of sodium azide and metal oxide (Fe203). The metal oxide functions a~ an oxidizer converting sodium azide to sodium oxide and nitrogen as shown in the following equation~:
6 NaN3 + Fe23 --~ 3 Na20 + 2 Fe + 9 N2 or 4 NaN3 + Fe23 - ~ 2 Na20 + Fe + Feo + 6 N2 The sodium oxide then reacts with the Feo forming sodium ferrite or with silicon dioxide (if present) to form ~odium silicate or with aluminum oxide to form sodium aluminate, as ~hown below:
Na20 + 2 Feo --~ 2 Na FeO2 (MP = 1347C) Na20 + siO2 --~ Na2 SiO3 (MP = 1088C) or 2 Na20 + SiO2 -~ Na4 SiO4 (MP = 1018C) Na20 + Al203 --~ 2 Na A102 (MP = 1650C) 206337~
However, the above reaction products melt at temperatures well below the combustion temperature of compositions described in this invention and would, therefore, be difficult to filter.
U.S. Patent No. 4,931,112 entitled, "Gas Generating Compositions Containing Nitrotriazalone discloses the use of nitrotriazolone (NTO) in combination with nitrates and nitrites of alkali metals (except sodium) and the alkaline earth metals calcium, strontium or barium. However, the compositions taught in the patent are not capable of forming useful solid clinkers. For example, the two compositions given in Example 2 consist of different ratios of NTO and strontium nitrate which, upon combustion, would produce strontium oxide and strontium carbonate as fine dust since there is no low-temperature slag former present.
Compositions claimed, utilizing mixtures of NTO and potassium nitrate, likewise will not form a useful solid clinker ~ince potassium carbonate would be produced which would be a liquid at the combustion temperature and no high temperature slag former is present. The hydroxide~ mentioned are very unlikely to be formed because the excess carbon dioxide would convert the metal oxides to carbonates in preference to hydroxides. Even if some hydroxides were formed they would be the wrong type of slag former to promote clinker formation.
U.S. Patent 4,909,549 entitled, "Composition and Process for Inflating a Safety Crash Bag" discloses the use of alkali metal salts, alkaline earth metal salts or ammonium salt of a hydrogen containing tetrazole in the range of about 20 to about 65 wt.~.
The effectiveness of alkali metal compounds, at these or lower concentrations, was not known.
SUMMARY OF THE INVENTION
The primary advantage of a new nonazide gas generant composition in accordance with the instant invention is that solid combustion products are easily filtered from the gas produced. The nonazide ga~
generant uses tetrazoles or tetrazole salts as the fuel and nitrogen source. The unique feature of thi~
invention is the novel use of oxidizers and additives resulting in solid combustion products which coalesce into easily filtered slag or clinkers.
Also, the gas generant compo~itions comprising this invention provide a relatively high yield of gas (moles of gas per gram of gas generant) compared to conventional occupant restraint gas generants.
Another primary advantage of a preferred embodiment of this invention is that the NOx is controlled by means which are effective even though a limited amount of excess oxygen is present. This allows reduction of the CO level by the exces~ oxygen while, at the same time, lowering the NOx concentration to acceptable values.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION
Since the ability to rapidly produce inflation gas which is relatively free of solid particulate q 2063374 matter is a requirement for automobile occupant restraint systems, even relatively nontoxic solids must be reduced to low levels. Almost any gas-~olid mixture can be filtered to produce clean gas if a large expensive filter can be used. However, for automobile occupant restraint systems both filter ~ize and cost must be minimized. The best way to accomplish this end is to produce solid combustion products which coalesce into large, easily filtered "clinkers" or slag.
Many combinations of ingredients can be used to improve the filtering characteristics of the combu~tion products. For most practical applications, however, compromises are necessary to provide the desired combination of slag forming ability, burn rate, ga~ production, gas quality, pellet forming characteristics, and other processing factors.
In accordance with the instant invention, several combinations of materials have been found which, produce easily filtered solid products as well as gases useful for inflation purposes. Such materials may be categorized as fuels, oxidizers, high-temperature ~lag formers and low-temperature slag formers. It is important that at least one material identified with each category be included in the mixture although certain materials can serve more than one of the categories as described below.
In formulating a fuel for the gas generant of an automobile occupant restraint system, it is de~irable to maximize the nitrogen content of the fuel and regulate the carbon and hydrogen content thereof to moderate values. Although carbon and hydrogen may be oxidized to carbon dioxide and water, which are relatively nontoxic gases, large amounts of heat are generated in the process.
Tetrazole compounds such as aminotetrazole, tetrazole, bitetrazole and metal salts of these compounds as well as triazole compounds such as 1,2,4-triazole-5-one or 3-nitro-1,2,4-triazole-5-one and metal salts of these compounds are especially useful fuels.
It should be noted that certain metal salts (alkaline earth metals) of these compounds can function, at least in part, as high temperature slag formers. For example, the calcium salt of tetrazole or bitetrazole forms, upon combustion, calcium oxide which would function as a high-temperature slag former.
Magnesium, strontium, barium and possibly cerium salts would act in ~imilar manner. In combination with a low-temperature slag former, a filterable slag would be formed. The alkali metal salts (lithium, sodium, potassium) could be considered, at least in part, as low-temperature slag formers since they could yield lower melting silicates or carbonates upon combustion.
Oxidizers generally supply all or most of the oxygen present in the system. In addition, however, they are the preferred method of including a high-temperature slag former into the reaction system.
The alkaline earth and cerium nitrates are all oxidizers with high-temperature slag forming potential, although most of these salts are hygroscopic and are difficult to use effectively. Strontium and barium nitrates are easy to obtain in the anhydrous state and are excellent oxidizers. Alkali metal nitrates, chlorates and perchlorates are other useful oxidizers when combined with a high-temperature slag former.
Materials which function as high-temperature slag formers have melting points at, or higher, than the combustion temperature or decompose into compounds which have melting point~, at or higher, than the combustion temperature. The alkaline earth oxides, hydroxides and oxalates are useful high-temperature slag formers. Magnesium carbonate and magnesium hydroxide are very useful high-temperature slag formers because they decompose before melting to form magnesium oxide which has a very high melting point (2800C). As mentioned above, oxidizers such as strontium nitrate are especially beneficial since they serve both as high-temperature slag former and oxidizer, thereby increasing the amount of gas produced per unit weight.
Metal salts as fuels, such as the calcium or strontium salt of 5-aminotetrazole, tetrazole, or ditetrazole are also useful high-temperature slag formers, although not as efficient as the oxidizers.
Other metal oxides having high melting points such as the oxides of titanium, zirconium and cerium are also useful high-temperature slag formers.
Materials which function as low-temperature slag formers have melting points at or below the combustion temperature or form compounds during combustion which have melting points at or below the 206337~
combustion temperature. Compounds such as silicon dioxide (SiO2), boric oxide (B203), vanadium pentoxide (V20s), sodium silicate (Na2 SiO3), potas~ium silicate (K2SiO3), sodium carbonate (Na2 C03) and potassium carbonate (K2C03) are examples of low-temperature slag formers.
It should be noted that either the oxidizer or the fuel can act as a low-temperature slag former if it contain~ a suitable substance which can be converted during combustion. For example, sodium nitrate or the sodium salt of tetrazole, during the combustion reactions, can convert to sodium carbonate or sodium silicate, if silicon dioxide is also present.
It is desirable to combine the fuel or oxidizer (or both) and the high temperature slag former into one ingredient, as shown in Example 1, where the strontium nitrate serves as both the oxidizer and high-temperature slag former. In this case, the strontium nitrate will yield, upon combustion, strontium oxide (SrO), which has a high melting point (2430C) as well as oxygen and nitrogen gases. Silicon dioxide, used as a low-temperature slag former is available in many forms ranging from very fine submicron particles to coarse ground sand with melting points from about 1500 to 1700C. The combination of strontium oxide and silicon dioxide forms strontium silicate (SrSiO3) with a melting point of approximately 1580C.
- SrO + SiO2 -~ SrSiO3 -20fi3~7 Strontium oxide can also react with carbon dioxide, forming strontium carbonate which melts at approximately 1500C at high pressure.
SrO + C02 --~ SrC03 The extent of each of these reactions depends upon various conditions such as combustion temperature, pressure, particle size of each component, and the contact time between the various materials.
It i8 believed that the function of the low-temperature slag former is to melt and glue the high-temperature solid particles together. With only low-temperature re~idue, the material is liquid and is difficult to filter. With only high-temperature materials, finely divided particles are formed which are also difficult to filter. The objective is to produce just enough low-temperature material to induce a coherent mass or slag to form, but not enough to make a low viscosity liquid.
Set in the above context, the pyrotechnic, slag forming gas generating mixture of the present invention comprises at least one each of the following materials.
a. A fuel selected from the group of tetrazole compounds consisting of aminotetrazole, tetrazole, bitetrazole and metal salts of these compounds as well as triazole compounds and metal - salts of triazole compounds.
206337~L `
l~( b. An oxygen containing oxidizer compound selected from the group consisting of alkali metal, alkaline earth metal, lanthanide and ammonium nitrates and perchlorates or from the group consisting of alkali metal or alkaline earth metal chlorates or peroxides.
c. A h$gh temperature slag forming material selected from the group consisting of alkaline earth metal or transition metal oxides, hydroxides, carbonates, oxalates, peroxides, nitrates, chlorates and perchlorates or from the group consisting of alkaline earth metal salts of tetrazoles, bitetrazoles and triazoles.
d. A low-temperature slag forming material selected from the group consisting of silicon dioxide, boric oxide and vanadium pentoxide or from the group consisting of alkali metal silicates, borates, carbonates, nitrates, perchlorates or chlorates or from the group consisting of alkali metal salts of tetrazoles, bitetrazoles and triazoles or from the group consisting of the various naturally occurring clays and talcs.
In practice, certain of the material~ may be substituted or interchanged. Specifically, both the fuel and the high-temperature slag forming material may 2063~7~
be selected from the group consisting of alkaline earth metal salts of tetrazoles, bitetrazoles and triazoles.
Both the oxygen containing oxidizer compound and high-temperature slag forming material may be comprised of one or more of the group consisting of alkaline earth metal and lanthanide nitrates, perchlorates, chlorates and peroxides. Both the fuel and the low-temperature slag forming material may comprise one or more of the group consisting of alkali metal salts of tetrazoles, bitetrazoles and triazoles. Both the oxygen containing oxidizer compound and the low-temperature slag forming material may comprise one or more of the group consisting of alkali metal nitrate~, perchlorates, chlorates and peroxides.
The fuel may comprise 5-aminotetrazole which is present in a concentration of about 22 to about 36~
by weight, where the oxygen containing oxidizer compound and high-temperature slag former is strontium nitrate which is present in a concentration of about 38 to about 62~ by weight, and said low-temperature slag former is silicon dioxide which is present in a concentration of about 2 to about 18% by weight.
Alternatively, the fuel and high-temperature slag forming material may comprise the strontium salt of 5-aminotetrazole which is present in a concentration of about 30 to about 50~ by weight, where the oxygen containing oxidizer compound is potassium nitrate which is present in a concentration of about 40 to about 60%
by weight,-~and the low-temperature slag former is talc 1~
which is present in a concentration of about 2 to about 10~ by weight. The talc may be replaced by clay.
Another combination comprises the 5-aminotetrazole which is present in a combination of about 22 to about 36~ by weight, where the oxygen containing oxidizer compound is sodium nitrate which is present in a concentration of about 30 to about 50~ by weight, the high-temperature slag forming material is magnesium carbonate which is present in a concentration of about 8 to about 30~ by weight, and the low-temperature slag former is silicon dioxide which is present in a concentration of about 2 to about 20~ by weight. Magnesium carbonate may be replaced by magnesium hydroxide.
Yet another combination comprises the pota~sium salt of 5-aminotetrazole which is present in a concentration of about 2 to about 30~ by weight which serves in part as a fuel and in part as a low-temperature slag former and wherein 5-aminotetrazole in a concentration of about 8 to about 40~ by weight also serve~ as a fuel, and wherein clay in a concentration of about 2 to about 10~ by weight serves in part as the low-temperature slag former and wherein strontium nitrate in a concentration of about 40 to about 66~ by weight serves as both the oxygen containing oxidizer and high-temperature slag former.
In another preferred embodiment, the invention comprises a pyrotechnic gas generating mixture of the type descri~bed comprising at least one material of each of the following functional groups of materials:
206337~
i 7 a fuel, an oxygen containing oxidizer compound, a chemical additive, and a low temperature slag forming material.
The fuel is selected from the group of azole compounds consisting of triazole, tetrazolone, aminotetrazole, tetrazole, bitetrazole and metal salts of these compounds. The oxygen containing oxidizer compound is selected from the group consisting of alkaline earth metal nitrates. The chemical additive is an alkali metal salt of an inorganic acid or organic acid selected from the group consisting of carbonate, triazole, tetrazole, 5-aminotetrazole, bitetrazole, and 3-nitro-1,2,4-triazol-5-one, said chemical additive being present in said mixture in an amount sufficient to reduce the amount of toxic oxides of nitrogen from the combustion products produced by the mixture under combustion. The low-temperature slag forming material is selected from the group consisting of naturally occurring clays, talcs or silicas.
One preferred composition is one wherein the fuel comprises 5-aminotetrazole in a concentration of about 28 to about 32~ by weight, the oxygen containing oxidizer compound comprises strontium nitrate in a concentration of about 50 to about 55~ by weight, the chemical additive comprises potassium carbonate in a concentration of about 2 to about 10~ by weight, and the low-temperature slag former comprises clay in a concentration of about 2 to about 10~ by weight.
Ig Another preferred composition is one wherein the fuel comprises 5-aminotetrazole in a concentration of about 26 to about 32% by weight, the oxygen containing oxidizer compound comprises strontium nitrate in a concentration of about 52 to about 58~ by weight, the chemical additive comprises sodium tetrazole in a concentration of about 2 to about 10~ by weight, and the low-temperature slag former comprises clay in a concentration of about 2 to about 10% by weight.
Still another preferred composition is one wherein the fuel comprises 5-aminotetrazole in a concentration of about 26 to about 32% by weight, the oxygen containing oxidizer compound comprises strontium nitrate in a concentraton of about 52 to about 58~ by weight, the chemical additive comprises the potassium salt of 5-aminotetrazole in a concentration of about 2 to about 12~ by weight, and the low-temperature slag former comprises talc in a concentration of about 2 to about 16~ by weight.
The invention importantly provides means of reducing the amount of the toxic gase~ NOx and CO in gas generant combu~tion products. This is accomplished by using an alkali metal salt mixed into the propellant. The primary effect of the salt is to reduce the amount of NOx but this allows formulation of the gas generant to provide an exce~s of oxygen, in the combustion products, which reduces the amount of carbon monoxides-as well as the NOx.
2063:~7 lq The invention contemplates application of these means to any gas generant which produces NOx and carbon monoxide.
The type of alkali metal compound used is important. While all alkali metals are likely to be effective in controlling NOx, potassium is the most preferred alkali metal because of its availability, low cost and effectiveness. The alkali metal preferably should be incorporated into the propellant as part of an organic compound rather than an inorganic compound.
Potassium carbonate also is effective. The preferred method of incorporating alkali metals into gas generants is as salts of organic acids. For gas generants used in automobile airbags it is advantageous to use compounds which have a high nitrogen content such as alkali metal salts of tetrazoles or triazoles.
These materials serve multiple functions when incorporated into a gas generant. In addition to reducing the amount of NOx produced, these compounds serve as fuels which produce useful gases and as low temperature ~lag formers as described elsewhere herein.
The range of alkali metal compounds which can be effectively used in a gas generant is quite broad.
As little as 2~ K5AT has been found to be effective as an additive and, in cases where the K5AT served as the primary fuel and gas producer, up to about 45~ has been used. The preferred range, however, i~ about 2 to about 20~ and the most preferred range is from about 2 to about 1~2~ by weight.
1a Regarding the ch~mi~l additive, as in~ tP~, the organic acid salts and carbonates are ~rr~clive. The salts of organic acids are most erreclive and are therefore p~er~lled. The alkali mePl salts of 5-aminotetra_ole, tetra7~1e, bitetr~7cle and 3-nitro-1,2,4-triazole-5-one (NTO) are ~ef~llc;d because of their high ni~ogell content. T ithillm, sodium and potassium are prer~llcd alkali metals; the invention also conlç~ tçs the use of rubidium and cç~illm The most plt;f~ d alkali metal is pot~ lm and the most ~lt;felled salt is the poP~illm salt of S-aminotetrazole.
The invention is illustrated by the following repr~ ;ve examples.
A llli~lU~ of 5-aminotetrazole (5AT) S~VI tiulll nitrate and silicon dioxide (silica) was p~epa~d having the following composition in percent by weight: 33.1% 5AT, 58.9%
strontium nitrate and 8% silica (Hi-sil* 233). These powders were dry blended and pellets were p~pa~ed by colll~ssion molding. When ignited with a propane-oxygen torch, these pellets burned rapidly and left a coherent, well formed, solid residue.
A ll~L~lult; of SAT, ~LIollliulll nitrate and benlonile clay was plepa,ed having the following composition in percent by weight: 33.1% 5AT, 58.9% ~lonliuln nitrate and 8%
clay. These powders were pre~alc;d and tested as in Example 1 with essenti~lly itl~ntic~l results.
*Trade-mark JJ:vs 20 Xi EXAMPLE 3 Zl A mixture of 5AT, strontium nitrate and boric oxide was prepared having the following composition in percent by weight: 33.1~ 5AT, 58.9~ strontium nitrate and 8~ boric oxide (B203)- These powders were dry blended and pellets were prepared by compression molding. When ignited with a propane-oxygen torch these pellets burned at a moderate rate and left a solid, partially porous residue.
A mixture of 5AT, sodium nitrate, iron oxide and silicon dioxide was prepared having the following composition in percent by weight: 26.7~ 5AT, 39.3 sodium nitrate, 29.3~ iron oxide (Fe203) and 4.7~
silicon dioxide. The iron oxide used was Mapico Red 516 Dark and the silicon dioxide was Hi-sil 233. These powders were dry blended and pellets were formed by compre~sion molding. When ignited with a propane-oxygen torch, the pellets burned smoothly leaving behind an expanded solid foam residue. When the pellets were burned in a Parr combustion bomb at an initial pressure of 25 atmospheres, a solid, coherent relatively hard residue was formed.
A mixture of 5AT, sodium nitrate, strontium nitrate and silicon dioxide was prepared having the following composition in percent by weight: 33.0~ 5AT, 10.0~ sodium nitrate, 49.0~ strontium nitrate and 8.0~
silicon d~oxide (Hi-sil 233). These powders were dry-blended and pellets were formed by compression molding. When ignited with a propane-oxygen torch, the pellets burned rapidly and left a hard, solid residue.
The burning rate of this composition was found to be 0.70 inch per second at 1000 psi. The burning rate was determined by measuring the time required to burn a cylindrical pellet of known length. The pellets were compression molded in a l/2-in. diameter die at approximately 16,000 pounds force, and were then coated on the sides with an epoxy/titanium dioxide inhibitor which prevented burning along the sides.
A mixture of 5AT, sodium nitrate, magnesium carbonate and silicon dioxide was prepared having the following composition in percent by weight: 29.6% 5AT, 40.4% sodium nitrate, 25.5% magnesium carbonate and 4.5~ silicon dioxide. These powders were dry-blended and pellets were formed by compression molding. When ignited with a propane-oxygen torch, the pellets burned smoothly and left a solid, hard residue.
Example 6 was repeated except that magnesium hydroxide was substituted for magnesium carbonate.
Pellets were prepared and burned with essentially identical results.
A mixture of 1,2,4-triazole-5-one (TO), strontium nitrate and silicon dioxide was prepared having the following composition in percent by weight;
27.6% TO, 64.4% strontium nitrate and 8.0% silicon dioxide (~i-sil 233). These powders were dry-blended and pellets were formed by compression molding. When ~ 2063374 ignited with a propane-oxygen torch, the pellets burned ~moothly and left a solid, partially porous residue.
Table I define~ the role of the various ingredients and identifie~ approximate range~ (in weight percent) of each ingredient for the above example~.
TABLE I
. _ . . . _ ., Exsmplo Hl~hTomporcluro LowTomporaluro Probablo No.~osclDnl~ Sl~oFormor SI~Form~r Slag Compononls 1,SAT (2~36) Sr (NO3)2 Sr (NO3)2 SiO2 S~O
S102 ~38~2) (2-18) Sr CO3 Sr SiO3 2.SAT ~22-36) Sr (NO3)2 Sr (NO3)2 Clay SrO
Clay (38~2) (2-18) Sr C03 S~ sio, O~cr silicalcs 3. SATC2~36) Sr (IYO3)2 Sr ~NO3)2 B203 St B20~
B2OJ (38~2) (2-18) Sr B~07 Sr CO3 4.SAT ~22-30) NaN03 FC23 (10 40) NaN03(30-50) Na2SiO3 Fc203 S1O2 (2-20) Na2CO3 SiO2 Na Fc02 FcO
SAT (2~36) 5NoNO3 Sr ~NO3)2 (8~) NaNO3 (0~2) Na2SiO3 Sr ~NO3)2 SiO2 (2-20) Na2 COJ
S;2 SrO
SrC03 Sr S103 SAT ~22-36) 6.1~03 MgCO3 ~8-30) NaN03 (30-S0) Na2SiO3 ~SgCO3 SiO2 (2-20) Na2 CO~
Sl02 M6 siO~
M~O
S;02 SAT (2W6) 7,NaNO3 Mg(OH)2 (8-30) N~NO3 (30-50) Mg SIO~
Mg(0~2 SiO2 (2-20) MgO
sio2 sio2 TO-(2~34) 8Sr (NO3 h Sr (NO3)2 SiO2 SrO
SiO2 (40-78) (2-20) Sr CO3 Sr SiO3 EXAMPLE 9 ~ ~
A mixture of 5-aminotetrazole (5AT), strontium nitrate (SrN) and bentonite clay was prepared having the following composition in percent by weight: 33.1~
5AT, 58.9~ SrN and 8.0~ clay. These powders were dry blended and pellets were formed by compression molding.
The pellets were burned in a Parr combustion bomb which was pressurized to 25 atmospheres pressure with nitrogen after flu~hing with nitrogen to remove any oxygen from the bomb. The pellets were ignited by means of a hot wire. A gas sample was removed from the bomb within lO seconds after combustion of the gas generant in order to minimize interaction of NOx with the solid combustion products. Analysis of the gas sample showed the presence of a relatively high concentration of NOx: 2180 parts per million (ppm) of NOx.
A mixture of 5AT, SrN, bentonite clay and the potassium salt of 5AT (K5AT) was prepared having the following composition in percent by weight: 28.6% 5AT, 57.4~ SrN, 8.0~ clay and 6.0~ K5AT. This mixture was calculated by a chemical equilibrium computer program to have a small excess of oxygen in the resulting gas mixture. The above powders were prepared and tested as described in Example 9. Two tests were performed resulting in measured NOx concentrations of 32 and 40 ppm. Example 10, by contrast with Example 9, illustrates the large reduction in NOx concentration produced by the addition of K5AT.
A mixture of 5AT, SrN, bentonite clay and potassium carbonate was prepared having the following composition in percent by weight: 31.1~ 5AT, 55.4~
SrN, 7.5~ clay and 6.0~ pota~sium carbonate. This mixture was prepared and tested as described in Example 9. Two tests were performed resulting in measured NOx concentrations of 128 and 80 ppm.
A mixture of 5AT, SrN, clay and the sodium salt of tetrazole (NaT) was prepared having the following composition in percent by weight: 30.4~ 5AT, 54.2~ SrN, 7.4~ clay and 8.0% NaT. This mixture was prepared and tested as described in Example 9. Two tests were performed resulting in measured NOx concentrations of 40 and 32 ppm.
A mixture of 5AT, potassium nitrate (KN), Talc and K5AT was prepared having the following composition in percent by weight: 25.2~ 5AT, 52.8KN, 16.0~ Talc and 6.0~ K5AT. This composition results in 2.5~ by volume excess oxygen as calculated by a chemical equilibrium computer program. Small pellets of thi~
mixture were prepared on an automatic tableting press.
These pellets were tested as described in Example 9.
Two tests were performed resulting in 112 ppm NOx and 100 ppm carbon monoxide in the first test and 144 ppm NOx and 140 ppm carbon monoxide in the second test. This example illustrates that low concentrations of both NOx and carbon monoxide can be obtained by using K5AT in combination with excess oxygen.
While the preferred embodiment of the invention has been disclosed, it should be appreciated that the invention is susceptible of modification without departing from the scope of the following claims.
Field Of The Invention Gas genpr~ting colllpositions for infl~ting occllp~nt lc~ t devices of over-the-road vehicles have been under development worldwide for many years and numerous patents have been granted thereon. l~ se of strict requirements relating to toxicity of the infl~tin~ gases, most gas generants now in use are based on inorganic azides, and especially sodium azide. One advantage of such known sodium azide gas generants is that the solid combustion products thereof generally produce a slag or "clinkers" which are easily filtered, resulting in a relatively clean gas. The ability of a gas generant to form a slag is a great advantage when the gases are used for inflation purposes, especi~lly when the gases must be filtered as in the inflation of an automobile oc~;up~nl fcslldint bag.
However, the use of the sodium azide, or other azides as a practical matter, results in extra expense and risk in gas generant m~mlf~ctllre due to the extreme JJ:vs toxicity of unfired azides. In addition, the potential hazard and disposal problem of unfired inflation devices must be considered. Thus, a nonazide gas generant exhibits a significant advantage over an azide-based gas generant because of such toxicity related concerns.
A fundamental problem that must be solved when using nonazide based gas generants is that it is easier to formulate slagging gas generants based on sodium azide than nonazide types because the combustion temperature is relatively low with azide-based gas generants. For example, the combustion temperature of a sodium azide/iron oxide slagging type generant is 969C (1776F) whereas, nonazide slagging type generants heretofore known have exhibited a combustion temperature of 1818C (3304F). Moreover, many common solid combustion products which might be expected from nonazide gas generants are liquids at the combustion temperature exhibited and are therefore difficult to filter out of the gas stream. For example, potassium carbonate melts at 891C and sodium silicate melts at approximately 1100C.
The formation of solid combustion products which coalesce at high combustion temperatures, and at high gas flow rates, requires a special combination of materials. Early attempts at formulating nonazide gas generants resulted in semi-solid combustion products that were difficult to filter. It has been found that combustion products which are liquid at the combustion temperature must be cooled until solidified before _ 3 filtering is successful because liquid products penetrate and clog the filter. It has also been found that cooling of the liquid combustion products results in cooling of the gas, which require~ the use of more gas generant. A cooled gas is relatively less efficient for inflation purposes, especially with an aspirator system. The additional gas generant, in turn, requires more cooling and an additional filter as well as a larger combustion chamber.
Mo~t azide-free, gas generant compositions provide a higher yield of gas (moles of gas per gram of gas generant) than conventional occupant restraint gas generants.
Although azide-free gas generating compositions offer numerous advantages over azide-based gas generants, it has been found difficult to produce gases which have sufficiently low levels of toxic substances. The toxic gases which are the most difficult to control are the oxides of nitrogen (NOx) and carbon monoxide (CO).
Most azide-free gas generants consi~t of carbon and nitrogen containing ingredientY which, upon combu~tion, produce small, but undesirable levels of NOx and CO in addition to the desired products, nitrogen and carbon dioxide.
In combustion processes involving compoundq containing both nitrogen and carbon it is possible to reduce or eliminate the CO by increasing the ratio of oxidizer to fuel. In this case, the extra oxygen oxidizes the CO to carbon dioxide. Unfortunately, 2063~74 L~
however, this approach results in increa~ed amount~ of NOx.
The ratio of oxidizer to fuel may also be lowered to eliminate excess oxygen and provide a fuel rich condition which reduces the amount of NOx produced. This approach, however, results in increased amounts of CO.
Even though it is possible, by means of chemical equilibrium calculationq, to find conditions of temperature~, pressure and gas generant compo~ition which could reduce both NOx and CO to nontoxic levels it has been very difficult to accomplish this result in actual practice.
The aforesaid problems are solved by the present invention, which discloses several type~ of nonazide ga~ generants that yield solid combustion products which form a ~lag or clinkers at the relatively high combustion temperature~ encountered with nonazide gas generants. The gas generants disclosed herein allow the u~e of ~imple, relatively inexpensive filter~ which cool the gas less and result in better pumping in an aspirated ~ystem. Taken together, these factor~ result in a simpler, less ëxpen~ive and smaller airbag inflation sy~tem.
A problem solved by a preferred embodiment of this invention i~ that the NOx is controlled by mean~
which are effective even though a limited amount of excess oxygen i8 present. This allows reduction of the CO level by the exce~s oxygen while, at the same time, lowering the NOx concentration to acceptable values.
DESCRIPTION OF THE PRIOR ART
An example of prior art teaching~ relating to the ~ubject matter of the instant invention is found in European Patent No. 0,055,547 entitled, "Solid Composition~ for Generating Nitrogen, The Generation of Nitrogen Therefrom and Inflation of Ga~ Bag~
Therewith". Thiq patent describes use of alkali or alkaline earth metal salt~ of a hydrogen-free tetrazole compound and oxidizerq of sodium nitrate, sodium nitrite and pota~qium nitrate or alkaline earth nitrates. A filter design is disclosed which utilizeq fiberglass fabric that forms a tacky surface for particle entrapment. The filter ha~ regions which cool and conden~e combustion solids. It iq obvious from the disclo~ure and from the nature of the ga~ generating compositions that the qolids produced do not form a qlag and are difficult to filter.
European Patent No. 0,055,904 entitled, "Azide Free Compo~ition~ for Generating Nitrogen, The Generation of Nitrogen Therefrom and Inflation of Ga~
Bag~ Therewith" deqcribes a filter used for particle entrapment. Oxidizers which contain no oxygen are used, and no mention of slag formation is made.
German Patent 2,004,620 teaches compoqitions of organic qalt~ (aminoguanidine) of ditetrazole and azotetrazole that are oxidized using oxidizers such as barium nitrate or potassium nitrate. However, no compo~itions are mentioned which would lead to ~lag formation.
U S. Patent 3,947,300 entitled, "Fuel for Generation of Nontoxic Propellant Gases" discloses the use of alkali or alkaline earth metal azides that can be oxidized by practically any stable anhydrous oxidizing agent. The ratio of ingredients is selected to assure the formation of glasQ-like silicates with "as low a melting or softening point as possible"
(column 2, lines 62-63 and column 4, lines 67-68).
These silicates would be very difficult to filter in a high temperature system.
U.S. Patent 4,376,002 entitled, "Multi-Ingredient Gas Generators" teaches the use of sodium azide and metal oxide (Fe203). The metal oxide functions a~ an oxidizer converting sodium azide to sodium oxide and nitrogen as shown in the following equation~:
6 NaN3 + Fe23 --~ 3 Na20 + 2 Fe + 9 N2 or 4 NaN3 + Fe23 - ~ 2 Na20 + Fe + Feo + 6 N2 The sodium oxide then reacts with the Feo forming sodium ferrite or with silicon dioxide (if present) to form ~odium silicate or with aluminum oxide to form sodium aluminate, as ~hown below:
Na20 + 2 Feo --~ 2 Na FeO2 (MP = 1347C) Na20 + siO2 --~ Na2 SiO3 (MP = 1088C) or 2 Na20 + SiO2 -~ Na4 SiO4 (MP = 1018C) Na20 + Al203 --~ 2 Na A102 (MP = 1650C) 206337~
However, the above reaction products melt at temperatures well below the combustion temperature of compositions described in this invention and would, therefore, be difficult to filter.
U.S. Patent No. 4,931,112 entitled, "Gas Generating Compositions Containing Nitrotriazalone discloses the use of nitrotriazolone (NTO) in combination with nitrates and nitrites of alkali metals (except sodium) and the alkaline earth metals calcium, strontium or barium. However, the compositions taught in the patent are not capable of forming useful solid clinkers. For example, the two compositions given in Example 2 consist of different ratios of NTO and strontium nitrate which, upon combustion, would produce strontium oxide and strontium carbonate as fine dust since there is no low-temperature slag former present.
Compositions claimed, utilizing mixtures of NTO and potassium nitrate, likewise will not form a useful solid clinker ~ince potassium carbonate would be produced which would be a liquid at the combustion temperature and no high temperature slag former is present. The hydroxide~ mentioned are very unlikely to be formed because the excess carbon dioxide would convert the metal oxides to carbonates in preference to hydroxides. Even if some hydroxides were formed they would be the wrong type of slag former to promote clinker formation.
U.S. Patent 4,909,549 entitled, "Composition and Process for Inflating a Safety Crash Bag" discloses the use of alkali metal salts, alkaline earth metal salts or ammonium salt of a hydrogen containing tetrazole in the range of about 20 to about 65 wt.~.
The effectiveness of alkali metal compounds, at these or lower concentrations, was not known.
SUMMARY OF THE INVENTION
The primary advantage of a new nonazide gas generant composition in accordance with the instant invention is that solid combustion products are easily filtered from the gas produced. The nonazide ga~
generant uses tetrazoles or tetrazole salts as the fuel and nitrogen source. The unique feature of thi~
invention is the novel use of oxidizers and additives resulting in solid combustion products which coalesce into easily filtered slag or clinkers.
Also, the gas generant compo~itions comprising this invention provide a relatively high yield of gas (moles of gas per gram of gas generant) compared to conventional occupant restraint gas generants.
Another primary advantage of a preferred embodiment of this invention is that the NOx is controlled by means which are effective even though a limited amount of excess oxygen is present. This allows reduction of the CO level by the exces~ oxygen while, at the same time, lowering the NOx concentration to acceptable values.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION
Since the ability to rapidly produce inflation gas which is relatively free of solid particulate q 2063374 matter is a requirement for automobile occupant restraint systems, even relatively nontoxic solids must be reduced to low levels. Almost any gas-~olid mixture can be filtered to produce clean gas if a large expensive filter can be used. However, for automobile occupant restraint systems both filter ~ize and cost must be minimized. The best way to accomplish this end is to produce solid combustion products which coalesce into large, easily filtered "clinkers" or slag.
Many combinations of ingredients can be used to improve the filtering characteristics of the combu~tion products. For most practical applications, however, compromises are necessary to provide the desired combination of slag forming ability, burn rate, ga~ production, gas quality, pellet forming characteristics, and other processing factors.
In accordance with the instant invention, several combinations of materials have been found which, produce easily filtered solid products as well as gases useful for inflation purposes. Such materials may be categorized as fuels, oxidizers, high-temperature ~lag formers and low-temperature slag formers. It is important that at least one material identified with each category be included in the mixture although certain materials can serve more than one of the categories as described below.
In formulating a fuel for the gas generant of an automobile occupant restraint system, it is de~irable to maximize the nitrogen content of the fuel and regulate the carbon and hydrogen content thereof to moderate values. Although carbon and hydrogen may be oxidized to carbon dioxide and water, which are relatively nontoxic gases, large amounts of heat are generated in the process.
Tetrazole compounds such as aminotetrazole, tetrazole, bitetrazole and metal salts of these compounds as well as triazole compounds such as 1,2,4-triazole-5-one or 3-nitro-1,2,4-triazole-5-one and metal salts of these compounds are especially useful fuels.
It should be noted that certain metal salts (alkaline earth metals) of these compounds can function, at least in part, as high temperature slag formers. For example, the calcium salt of tetrazole or bitetrazole forms, upon combustion, calcium oxide which would function as a high-temperature slag former.
Magnesium, strontium, barium and possibly cerium salts would act in ~imilar manner. In combination with a low-temperature slag former, a filterable slag would be formed. The alkali metal salts (lithium, sodium, potassium) could be considered, at least in part, as low-temperature slag formers since they could yield lower melting silicates or carbonates upon combustion.
Oxidizers generally supply all or most of the oxygen present in the system. In addition, however, they are the preferred method of including a high-temperature slag former into the reaction system.
The alkaline earth and cerium nitrates are all oxidizers with high-temperature slag forming potential, although most of these salts are hygroscopic and are difficult to use effectively. Strontium and barium nitrates are easy to obtain in the anhydrous state and are excellent oxidizers. Alkali metal nitrates, chlorates and perchlorates are other useful oxidizers when combined with a high-temperature slag former.
Materials which function as high-temperature slag formers have melting points at, or higher, than the combustion temperature or decompose into compounds which have melting point~, at or higher, than the combustion temperature. The alkaline earth oxides, hydroxides and oxalates are useful high-temperature slag formers. Magnesium carbonate and magnesium hydroxide are very useful high-temperature slag formers because they decompose before melting to form magnesium oxide which has a very high melting point (2800C). As mentioned above, oxidizers such as strontium nitrate are especially beneficial since they serve both as high-temperature slag former and oxidizer, thereby increasing the amount of gas produced per unit weight.
Metal salts as fuels, such as the calcium or strontium salt of 5-aminotetrazole, tetrazole, or ditetrazole are also useful high-temperature slag formers, although not as efficient as the oxidizers.
Other metal oxides having high melting points such as the oxides of titanium, zirconium and cerium are also useful high-temperature slag formers.
Materials which function as low-temperature slag formers have melting points at or below the combustion temperature or form compounds during combustion which have melting points at or below the 206337~
combustion temperature. Compounds such as silicon dioxide (SiO2), boric oxide (B203), vanadium pentoxide (V20s), sodium silicate (Na2 SiO3), potas~ium silicate (K2SiO3), sodium carbonate (Na2 C03) and potassium carbonate (K2C03) are examples of low-temperature slag formers.
It should be noted that either the oxidizer or the fuel can act as a low-temperature slag former if it contain~ a suitable substance which can be converted during combustion. For example, sodium nitrate or the sodium salt of tetrazole, during the combustion reactions, can convert to sodium carbonate or sodium silicate, if silicon dioxide is also present.
It is desirable to combine the fuel or oxidizer (or both) and the high temperature slag former into one ingredient, as shown in Example 1, where the strontium nitrate serves as both the oxidizer and high-temperature slag former. In this case, the strontium nitrate will yield, upon combustion, strontium oxide (SrO), which has a high melting point (2430C) as well as oxygen and nitrogen gases. Silicon dioxide, used as a low-temperature slag former is available in many forms ranging from very fine submicron particles to coarse ground sand with melting points from about 1500 to 1700C. The combination of strontium oxide and silicon dioxide forms strontium silicate (SrSiO3) with a melting point of approximately 1580C.
- SrO + SiO2 -~ SrSiO3 -20fi3~7 Strontium oxide can also react with carbon dioxide, forming strontium carbonate which melts at approximately 1500C at high pressure.
SrO + C02 --~ SrC03 The extent of each of these reactions depends upon various conditions such as combustion temperature, pressure, particle size of each component, and the contact time between the various materials.
It i8 believed that the function of the low-temperature slag former is to melt and glue the high-temperature solid particles together. With only low-temperature re~idue, the material is liquid and is difficult to filter. With only high-temperature materials, finely divided particles are formed which are also difficult to filter. The objective is to produce just enough low-temperature material to induce a coherent mass or slag to form, but not enough to make a low viscosity liquid.
Set in the above context, the pyrotechnic, slag forming gas generating mixture of the present invention comprises at least one each of the following materials.
a. A fuel selected from the group of tetrazole compounds consisting of aminotetrazole, tetrazole, bitetrazole and metal salts of these compounds as well as triazole compounds and metal - salts of triazole compounds.
206337~L `
l~( b. An oxygen containing oxidizer compound selected from the group consisting of alkali metal, alkaline earth metal, lanthanide and ammonium nitrates and perchlorates or from the group consisting of alkali metal or alkaline earth metal chlorates or peroxides.
c. A h$gh temperature slag forming material selected from the group consisting of alkaline earth metal or transition metal oxides, hydroxides, carbonates, oxalates, peroxides, nitrates, chlorates and perchlorates or from the group consisting of alkaline earth metal salts of tetrazoles, bitetrazoles and triazoles.
d. A low-temperature slag forming material selected from the group consisting of silicon dioxide, boric oxide and vanadium pentoxide or from the group consisting of alkali metal silicates, borates, carbonates, nitrates, perchlorates or chlorates or from the group consisting of alkali metal salts of tetrazoles, bitetrazoles and triazoles or from the group consisting of the various naturally occurring clays and talcs.
In practice, certain of the material~ may be substituted or interchanged. Specifically, both the fuel and the high-temperature slag forming material may 2063~7~
be selected from the group consisting of alkaline earth metal salts of tetrazoles, bitetrazoles and triazoles.
Both the oxygen containing oxidizer compound and high-temperature slag forming material may be comprised of one or more of the group consisting of alkaline earth metal and lanthanide nitrates, perchlorates, chlorates and peroxides. Both the fuel and the low-temperature slag forming material may comprise one or more of the group consisting of alkali metal salts of tetrazoles, bitetrazoles and triazoles. Both the oxygen containing oxidizer compound and the low-temperature slag forming material may comprise one or more of the group consisting of alkali metal nitrate~, perchlorates, chlorates and peroxides.
The fuel may comprise 5-aminotetrazole which is present in a concentration of about 22 to about 36~
by weight, where the oxygen containing oxidizer compound and high-temperature slag former is strontium nitrate which is present in a concentration of about 38 to about 62~ by weight, and said low-temperature slag former is silicon dioxide which is present in a concentration of about 2 to about 18% by weight.
Alternatively, the fuel and high-temperature slag forming material may comprise the strontium salt of 5-aminotetrazole which is present in a concentration of about 30 to about 50~ by weight, where the oxygen containing oxidizer compound is potassium nitrate which is present in a concentration of about 40 to about 60%
by weight,-~and the low-temperature slag former is talc 1~
which is present in a concentration of about 2 to about 10~ by weight. The talc may be replaced by clay.
Another combination comprises the 5-aminotetrazole which is present in a combination of about 22 to about 36~ by weight, where the oxygen containing oxidizer compound is sodium nitrate which is present in a concentration of about 30 to about 50~ by weight, the high-temperature slag forming material is magnesium carbonate which is present in a concentration of about 8 to about 30~ by weight, and the low-temperature slag former is silicon dioxide which is present in a concentration of about 2 to about 20~ by weight. Magnesium carbonate may be replaced by magnesium hydroxide.
Yet another combination comprises the pota~sium salt of 5-aminotetrazole which is present in a concentration of about 2 to about 30~ by weight which serves in part as a fuel and in part as a low-temperature slag former and wherein 5-aminotetrazole in a concentration of about 8 to about 40~ by weight also serve~ as a fuel, and wherein clay in a concentration of about 2 to about 10~ by weight serves in part as the low-temperature slag former and wherein strontium nitrate in a concentration of about 40 to about 66~ by weight serves as both the oxygen containing oxidizer and high-temperature slag former.
In another preferred embodiment, the invention comprises a pyrotechnic gas generating mixture of the type descri~bed comprising at least one material of each of the following functional groups of materials:
206337~
i 7 a fuel, an oxygen containing oxidizer compound, a chemical additive, and a low temperature slag forming material.
The fuel is selected from the group of azole compounds consisting of triazole, tetrazolone, aminotetrazole, tetrazole, bitetrazole and metal salts of these compounds. The oxygen containing oxidizer compound is selected from the group consisting of alkaline earth metal nitrates. The chemical additive is an alkali metal salt of an inorganic acid or organic acid selected from the group consisting of carbonate, triazole, tetrazole, 5-aminotetrazole, bitetrazole, and 3-nitro-1,2,4-triazol-5-one, said chemical additive being present in said mixture in an amount sufficient to reduce the amount of toxic oxides of nitrogen from the combustion products produced by the mixture under combustion. The low-temperature slag forming material is selected from the group consisting of naturally occurring clays, talcs or silicas.
One preferred composition is one wherein the fuel comprises 5-aminotetrazole in a concentration of about 28 to about 32~ by weight, the oxygen containing oxidizer compound comprises strontium nitrate in a concentration of about 50 to about 55~ by weight, the chemical additive comprises potassium carbonate in a concentration of about 2 to about 10~ by weight, and the low-temperature slag former comprises clay in a concentration of about 2 to about 10~ by weight.
Ig Another preferred composition is one wherein the fuel comprises 5-aminotetrazole in a concentration of about 26 to about 32% by weight, the oxygen containing oxidizer compound comprises strontium nitrate in a concentration of about 52 to about 58~ by weight, the chemical additive comprises sodium tetrazole in a concentration of about 2 to about 10~ by weight, and the low-temperature slag former comprises clay in a concentration of about 2 to about 10% by weight.
Still another preferred composition is one wherein the fuel comprises 5-aminotetrazole in a concentration of about 26 to about 32% by weight, the oxygen containing oxidizer compound comprises strontium nitrate in a concentraton of about 52 to about 58~ by weight, the chemical additive comprises the potassium salt of 5-aminotetrazole in a concentration of about 2 to about 12~ by weight, and the low-temperature slag former comprises talc in a concentration of about 2 to about 16~ by weight.
The invention importantly provides means of reducing the amount of the toxic gase~ NOx and CO in gas generant combu~tion products. This is accomplished by using an alkali metal salt mixed into the propellant. The primary effect of the salt is to reduce the amount of NOx but this allows formulation of the gas generant to provide an exce~s of oxygen, in the combustion products, which reduces the amount of carbon monoxides-as well as the NOx.
2063:~7 lq The invention contemplates application of these means to any gas generant which produces NOx and carbon monoxide.
The type of alkali metal compound used is important. While all alkali metals are likely to be effective in controlling NOx, potassium is the most preferred alkali metal because of its availability, low cost and effectiveness. The alkali metal preferably should be incorporated into the propellant as part of an organic compound rather than an inorganic compound.
Potassium carbonate also is effective. The preferred method of incorporating alkali metals into gas generants is as salts of organic acids. For gas generants used in automobile airbags it is advantageous to use compounds which have a high nitrogen content such as alkali metal salts of tetrazoles or triazoles.
These materials serve multiple functions when incorporated into a gas generant. In addition to reducing the amount of NOx produced, these compounds serve as fuels which produce useful gases and as low temperature ~lag formers as described elsewhere herein.
The range of alkali metal compounds which can be effectively used in a gas generant is quite broad.
As little as 2~ K5AT has been found to be effective as an additive and, in cases where the K5AT served as the primary fuel and gas producer, up to about 45~ has been used. The preferred range, however, i~ about 2 to about 20~ and the most preferred range is from about 2 to about 1~2~ by weight.
1a Regarding the ch~mi~l additive, as in~ tP~, the organic acid salts and carbonates are ~rr~clive. The salts of organic acids are most erreclive and are therefore p~er~lled. The alkali mePl salts of 5-aminotetra_ole, tetra7~1e, bitetr~7cle and 3-nitro-1,2,4-triazole-5-one (NTO) are ~ef~llc;d because of their high ni~ogell content. T ithillm, sodium and potassium are prer~llcd alkali metals; the invention also conlç~ tçs the use of rubidium and cç~illm The most plt;f~ d alkali metal is pot~ lm and the most ~lt;felled salt is the poP~illm salt of S-aminotetrazole.
The invention is illustrated by the following repr~ ;ve examples.
A llli~lU~ of 5-aminotetrazole (5AT) S~VI tiulll nitrate and silicon dioxide (silica) was p~epa~d having the following composition in percent by weight: 33.1% 5AT, 58.9%
strontium nitrate and 8% silica (Hi-sil* 233). These powders were dry blended and pellets were p~pa~ed by colll~ssion molding. When ignited with a propane-oxygen torch, these pellets burned rapidly and left a coherent, well formed, solid residue.
A ll~L~lult; of SAT, ~LIollliulll nitrate and benlonile clay was plepa,ed having the following composition in percent by weight: 33.1% 5AT, 58.9% ~lonliuln nitrate and 8%
clay. These powders were pre~alc;d and tested as in Example 1 with essenti~lly itl~ntic~l results.
*Trade-mark JJ:vs 20 Xi EXAMPLE 3 Zl A mixture of 5AT, strontium nitrate and boric oxide was prepared having the following composition in percent by weight: 33.1~ 5AT, 58.9~ strontium nitrate and 8~ boric oxide (B203)- These powders were dry blended and pellets were prepared by compression molding. When ignited with a propane-oxygen torch these pellets burned at a moderate rate and left a solid, partially porous residue.
A mixture of 5AT, sodium nitrate, iron oxide and silicon dioxide was prepared having the following composition in percent by weight: 26.7~ 5AT, 39.3 sodium nitrate, 29.3~ iron oxide (Fe203) and 4.7~
silicon dioxide. The iron oxide used was Mapico Red 516 Dark and the silicon dioxide was Hi-sil 233. These powders were dry blended and pellets were formed by compre~sion molding. When ignited with a propane-oxygen torch, the pellets burned smoothly leaving behind an expanded solid foam residue. When the pellets were burned in a Parr combustion bomb at an initial pressure of 25 atmospheres, a solid, coherent relatively hard residue was formed.
A mixture of 5AT, sodium nitrate, strontium nitrate and silicon dioxide was prepared having the following composition in percent by weight: 33.0~ 5AT, 10.0~ sodium nitrate, 49.0~ strontium nitrate and 8.0~
silicon d~oxide (Hi-sil 233). These powders were dry-blended and pellets were formed by compression molding. When ignited with a propane-oxygen torch, the pellets burned rapidly and left a hard, solid residue.
The burning rate of this composition was found to be 0.70 inch per second at 1000 psi. The burning rate was determined by measuring the time required to burn a cylindrical pellet of known length. The pellets were compression molded in a l/2-in. diameter die at approximately 16,000 pounds force, and were then coated on the sides with an epoxy/titanium dioxide inhibitor which prevented burning along the sides.
A mixture of 5AT, sodium nitrate, magnesium carbonate and silicon dioxide was prepared having the following composition in percent by weight: 29.6% 5AT, 40.4% sodium nitrate, 25.5% magnesium carbonate and 4.5~ silicon dioxide. These powders were dry-blended and pellets were formed by compression molding. When ignited with a propane-oxygen torch, the pellets burned smoothly and left a solid, hard residue.
Example 6 was repeated except that magnesium hydroxide was substituted for magnesium carbonate.
Pellets were prepared and burned with essentially identical results.
A mixture of 1,2,4-triazole-5-one (TO), strontium nitrate and silicon dioxide was prepared having the following composition in percent by weight;
27.6% TO, 64.4% strontium nitrate and 8.0% silicon dioxide (~i-sil 233). These powders were dry-blended and pellets were formed by compression molding. When ~ 2063374 ignited with a propane-oxygen torch, the pellets burned ~moothly and left a solid, partially porous residue.
Table I define~ the role of the various ingredients and identifie~ approximate range~ (in weight percent) of each ingredient for the above example~.
TABLE I
. _ . . . _ ., Exsmplo Hl~hTomporcluro LowTomporaluro Probablo No.~osclDnl~ Sl~oFormor SI~Form~r Slag Compononls 1,SAT (2~36) Sr (NO3)2 Sr (NO3)2 SiO2 S~O
S102 ~38~2) (2-18) Sr CO3 Sr SiO3 2.SAT ~22-36) Sr (NO3)2 Sr (NO3)2 Clay SrO
Clay (38~2) (2-18) Sr C03 S~ sio, O~cr silicalcs 3. SATC2~36) Sr (IYO3)2 Sr ~NO3)2 B203 St B20~
B2OJ (38~2) (2-18) Sr B~07 Sr CO3 4.SAT ~22-30) NaN03 FC23 (10 40) NaN03(30-50) Na2SiO3 Fc203 S1O2 (2-20) Na2CO3 SiO2 Na Fc02 FcO
SAT (2~36) 5NoNO3 Sr ~NO3)2 (8~) NaNO3 (0~2) Na2SiO3 Sr ~NO3)2 SiO2 (2-20) Na2 COJ
S;2 SrO
SrC03 Sr S103 SAT ~22-36) 6.1~03 MgCO3 ~8-30) NaN03 (30-S0) Na2SiO3 ~SgCO3 SiO2 (2-20) Na2 CO~
Sl02 M6 siO~
M~O
S;02 SAT (2W6) 7,NaNO3 Mg(OH)2 (8-30) N~NO3 (30-50) Mg SIO~
Mg(0~2 SiO2 (2-20) MgO
sio2 sio2 TO-(2~34) 8Sr (NO3 h Sr (NO3)2 SiO2 SrO
SiO2 (40-78) (2-20) Sr CO3 Sr SiO3 EXAMPLE 9 ~ ~
A mixture of 5-aminotetrazole (5AT), strontium nitrate (SrN) and bentonite clay was prepared having the following composition in percent by weight: 33.1~
5AT, 58.9~ SrN and 8.0~ clay. These powders were dry blended and pellets were formed by compression molding.
The pellets were burned in a Parr combustion bomb which was pressurized to 25 atmospheres pressure with nitrogen after flu~hing with nitrogen to remove any oxygen from the bomb. The pellets were ignited by means of a hot wire. A gas sample was removed from the bomb within lO seconds after combustion of the gas generant in order to minimize interaction of NOx with the solid combustion products. Analysis of the gas sample showed the presence of a relatively high concentration of NOx: 2180 parts per million (ppm) of NOx.
A mixture of 5AT, SrN, bentonite clay and the potassium salt of 5AT (K5AT) was prepared having the following composition in percent by weight: 28.6% 5AT, 57.4~ SrN, 8.0~ clay and 6.0~ K5AT. This mixture was calculated by a chemical equilibrium computer program to have a small excess of oxygen in the resulting gas mixture. The above powders were prepared and tested as described in Example 9. Two tests were performed resulting in measured NOx concentrations of 32 and 40 ppm. Example 10, by contrast with Example 9, illustrates the large reduction in NOx concentration produced by the addition of K5AT.
A mixture of 5AT, SrN, bentonite clay and potassium carbonate was prepared having the following composition in percent by weight: 31.1~ 5AT, 55.4~
SrN, 7.5~ clay and 6.0~ pota~sium carbonate. This mixture was prepared and tested as described in Example 9. Two tests were performed resulting in measured NOx concentrations of 128 and 80 ppm.
A mixture of 5AT, SrN, clay and the sodium salt of tetrazole (NaT) was prepared having the following composition in percent by weight: 30.4~ 5AT, 54.2~ SrN, 7.4~ clay and 8.0% NaT. This mixture was prepared and tested as described in Example 9. Two tests were performed resulting in measured NOx concentrations of 40 and 32 ppm.
A mixture of 5AT, potassium nitrate (KN), Talc and K5AT was prepared having the following composition in percent by weight: 25.2~ 5AT, 52.8KN, 16.0~ Talc and 6.0~ K5AT. This composition results in 2.5~ by volume excess oxygen as calculated by a chemical equilibrium computer program. Small pellets of thi~
mixture were prepared on an automatic tableting press.
These pellets were tested as described in Example 9.
Two tests were performed resulting in 112 ppm NOx and 100 ppm carbon monoxide in the first test and 144 ppm NOx and 140 ppm carbon monoxide in the second test. This example illustrates that low concentrations of both NOx and carbon monoxide can be obtained by using K5AT in combination with excess oxygen.
While the preferred embodiment of the invention has been disclosed, it should be appreciated that the invention is susceptible of modification without departing from the scope of the following claims.
Claims (25)
1. A pyrotechnic, gas generating mixture useful under combustion for inflating an automobile or aircraft safety crash bag, said pyrotechnic mixture comprising at least one material of each of the following functional groups of materials:
a. A fuel selected from the group of azole compounds consisting of triazole, aminotetrazole, tetrazole, bitetrazole, and metal salts of these compounds, b. An oxygen containing oxidizer compound selected from the group consisting of alkaline earth metal nitrates and perchlorates, and alkali metal nitrates and perchlorates, c. A chemical additive that is an alkali metal salt of an inorganic acid or organic acid selected from the group consisting of carbonate, triazole, tetrazole, 5-aminotetrazole, bitetrazole, and 3-nitro-1,2,4-triazole-5-one, said chemical additive being present in said mixture in an amount sufficient to reduce the amount of toxic oxides of nitrogen from the combustion products produced by the mixture under combustion, and d. A low-temperature slag forming material selected from the group consisting of naturally occurring clays and talcs and silica, with the proviso that said gas generating mixture lacks a high temperature slag forming material selected from the group consisting of alkaline earth metal oxides, hydroxides, carbonates, and oxalates, and with the further proviso that where the low temperature slag forming material comprises clay or silica, the pyrotechnic mixture does not in weight % contain the following:
5-aminotetrazole about 22 to about 36 Clay or SiO2 about 2 to about 18 Sr(NO3)2 about 38 to about 62 or 5-aminotetrazole about 22 to about 36 Sr(NO3)2 about 8 to about 62 NaNO3 0 to about 42 SiO2 about 2 to about 18 or 1,2,4-triazole-5-one about 20 to about 34 Sr(NO3)2 about 40 to about 78 SiO2 about 2 to about 20.
a. A fuel selected from the group of azole compounds consisting of triazole, aminotetrazole, tetrazole, bitetrazole, and metal salts of these compounds, b. An oxygen containing oxidizer compound selected from the group consisting of alkaline earth metal nitrates and perchlorates, and alkali metal nitrates and perchlorates, c. A chemical additive that is an alkali metal salt of an inorganic acid or organic acid selected from the group consisting of carbonate, triazole, tetrazole, 5-aminotetrazole, bitetrazole, and 3-nitro-1,2,4-triazole-5-one, said chemical additive being present in said mixture in an amount sufficient to reduce the amount of toxic oxides of nitrogen from the combustion products produced by the mixture under combustion, and d. A low-temperature slag forming material selected from the group consisting of naturally occurring clays and talcs and silica, with the proviso that said gas generating mixture lacks a high temperature slag forming material selected from the group consisting of alkaline earth metal oxides, hydroxides, carbonates, and oxalates, and with the further proviso that where the low temperature slag forming material comprises clay or silica, the pyrotechnic mixture does not in weight % contain the following:
5-aminotetrazole about 22 to about 36 Clay or SiO2 about 2 to about 18 Sr(NO3)2 about 38 to about 62 or 5-aminotetrazole about 22 to about 36 Sr(NO3)2 about 8 to about 62 NaNO3 0 to about 42 SiO2 about 2 to about 18 or 1,2,4-triazole-5-one about 20 to about 34 Sr(NO3)2 about 40 to about 78 SiO2 about 2 to about 20.
2. The composition of claim 1 wherein the fuel comprises 5-aminotetrazole which is present in a concentration of about 28 to about 32% by weight, said oxygen containing oxidizer compound comprises strontium nitrate which is present in a concentration of about 50 to about 55% by weight, said chemical additive comprises JJ:vs - 28 -potassium carbonate which is present in a concentration of about 2 to about 10% by weight, and said low-temperature slag former comprises clay which is present in a concentration of about 2 to about 10% by weight.
3. The composition of claim 1 wherein the fuel comprises 5-aminotetrazole which is present in a concentration of about 26 to about 32% by weight, said oxygen containing oxidizer compound comprises strontium nitrate which is present in a concentration of about 52 to about 58% by weight, said chemical additive comprises sodium tetrazole which is present in a concentration of about 2 to about 10% by weight, and said low-temperature slag former comprises clay which is present in a concentration of about 2 to about 10% by weight.
4. The composition of claim 1 wherein the fuel comprises
5-aminotetrazole which is present in a concentration of about 26 to about 32% by weight, said oxygen containing oxidizer compound comprises strontium nitrate which is present in a concentration of about 52 to about 58% by weight, said chemical additive comprises the potassium salt of 5-aminotetrazole which is present in a concentration of about 2 to about 12% by weight, and said low-temperature slag former comprises talc which is present in a concentration of about 2 to about 16% by weight.
5. The composition of claim 1 wherein the chemical additive is the alkali metal salt of 5-aminotetrazole.
5. The composition of claim 1 wherein the chemical additive is the alkali metal salt of 5-aminotetrazole.
6. The composition of claim 1 wherein the chemical additive is the alkali metal salt of tetrazole.
7. The composition of claim 1 where the chemical additive is the alkali metal salt of bitetrazole.
8. The composition of claim 1 wherein the chemical additive is the alkali metal salt of 3-nitro-1,2,4-triazol-5-one.
9. The composition of claim 1 wherein the chemical additive is the potassium, sodium or lithium salt of 5-aminotetrazole.
10. The composition of claim 1 wherein the chemical additive is the potassium, sodium or lithium salt of the tetrazole.
11. The composition of claim 1 wherein the chemical additive is the potassium, sodium or lithium salt of 3-nitro-1,2,4-triazol-5-one.
12. The composition of claim 1 wherein the chemical additive is present in a concentration of about 2% to about 45% by weight.
13. The composition of claim 1 wherein the chemical additive is an alkali metal carbonate.
14. The composition of claim 1 wherein the chemical additive is potassium carbonate.
15. A method of reducing or eliminating toxic oxides of nitrogen from the combustion of a gas generating mixture comprising fuel, oxidizer and slag forming material according to claim 1 comprising the step of including a chemical additive in said gas generating mixture comprising an alkali metal salt of an inorganic acid or organic acid selected from the group consisting of carbonate and azole.
16. The method of claim 15 wherein the chemical additive is the alkali metal salt of 5-aminotetrazole.
17. The method of claim 15 wherein the chemical additive is the alkali metal salt of tetrazole.
18. The method of claim 15 where the chemical additive is the alkali metal salt of bitetrazole.
19. The method of claim 15 wherein the chemical additive is the alkali metal salt of 3-nitro-1,2,4-triazol-5-one.
20. The method of claim 15 wherein the chemical additive is the potassium, sodium or lithium salt of 5-aminotetrazole.
21. The method of claim 15 wherein the chemical additive is the potassium, sodium or lithium salt of the tetrazole.
22. The method of claim 15 wherein the chemical additive is the potassium, sodium or lithium salt of 3-nitro-1,2,4-triazol-5-one.
23. The method of claim 15 wherein the chemical additive is present in a concentration of about 2% to about 45% by weight.
24. The method of claim 15 wherein the chemical additive is an alkali metal carbonate.
25. The method of claim 15 wherein the chemical additive is potassium carbonate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US685,316 | 1991-04-15 | ||
| US07/685,316 US5139588A (en) | 1990-10-23 | 1991-04-15 | Composition for controlling oxides of nitrogen |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2063374A1 CA2063374A1 (en) | 1992-10-16 |
| CA2063374C true CA2063374C (en) | 1997-02-11 |
Family
ID=24751659
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002063374A Expired - Fee Related CA2063374C (en) | 1991-04-15 | 1992-03-18 | Composition for controlling oxides of nitrogen |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5139588A (en) |
| EP (1) | EP0509763B1 (en) |
| JP (1) | JP2597066B2 (en) |
| KR (1) | KR960016589B1 (en) |
| AU (1) | AU639879B2 (en) |
| CA (1) | CA2063374C (en) |
| DE (1) | DE69220412T2 (en) |
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| KR101704757B1 (en) | 2014-11-25 | 2017-02-08 | 전남대학교산학협력단 | Manufacturing method of high purity mesoporous inorganic oxides and high purity mesoporous inorganic oxides made by the same |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4369079A (en) * | 1980-12-31 | 1983-01-18 | Thiokol Corporation | Solid non-azide nitrogen gas generant compositions |
| US4948439A (en) * | 1988-12-02 | 1990-08-14 | Automotive Systems Laboratory, Inc. | Composition and process for inflating a safety crash bag |
| US5035757A (en) * | 1990-10-25 | 1991-07-30 | Automotive Systems Laboratory, Inc. | Azide-free gas generant composition with easily filterable combustion products |
-
1991
- 1991-04-15 US US07/685,316 patent/US5139588A/en not_active Expired - Lifetime
-
1992
- 1992-03-18 CA CA002063374A patent/CA2063374C/en not_active Expired - Fee Related
- 1992-03-20 AU AU13058/92A patent/AU639879B2/en not_active Expired - Fee Related
- 1992-04-09 KR KR1019920005905A patent/KR960016589B1/en not_active IP Right Cessation
- 1992-04-14 DE DE69220412T patent/DE69220412T2/en not_active Expired - Fee Related
- 1992-04-14 EP EP92303343A patent/EP0509763B1/en not_active Expired - Lifetime
- 1992-04-15 JP JP4095425A patent/JP2597066B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0509763A1 (en) | 1992-10-21 |
| DE69220412T2 (en) | 1997-10-09 |
| CA2063374A1 (en) | 1992-10-16 |
| AU1305892A (en) | 1992-10-22 |
| JP2597066B2 (en) | 1997-04-02 |
| KR960016589B1 (en) | 1996-12-16 |
| AU639879B2 (en) | 1993-08-05 |
| JPH05117070A (en) | 1993-05-14 |
| EP0509763B1 (en) | 1997-06-18 |
| KR920019711A (en) | 1992-11-19 |
| DE69220412D1 (en) | 1997-07-24 |
| US5139588A (en) | 1992-08-18 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |